Noise causes people psychological discomfort, can be a source of irritation and stress, and can cause conditions such as headaches and hearing loss. As a result, a variety of countermeasures have been proposed. Countermeasures proposed in the past have exhibited a limited effect in terms of reducing the level of noise that encompasses all frequency regions, but these tackled noise by reducing sounds mainly in the middle frequency region and high frequency region.
Non-woven fabrics are fabrics produced by irregularly aligning or entangling natural or synthetic fibers through the use of adhesive agents, heating and pressing or sewing, and are highly porous materials having connected voids. If porous sound absorbing materials are thin, absorption of sound in the low frequency region is generally difficult. In the past, materials having a mass per unit area of 0.1-20 g/m2 (see Patent Document 1) and materials requiring a thickness of 0.5 mm or more (see Patent Document 2) have been reported as sound absorbing materials.